The present invention relates to an actuation device for the actuating of an adjustment surface of an aircraft such as an elevator, a rudder or the like, of landing gear or another aircraft or surface vehicle actuator, comprising an electrohydraulic actuator having a servo control cylinder, a pump for pressure fluid action on the servo control cylinder as well as an electric motor for the actuation of the pump, with the electric motor having a liquid cooling.
In aircraft, actuators such as elevators or ailerons are frequently actuated by means of a hydraulic cylinder which is connected to a central hydraulic supply via corresponding hydraulic lines. With such a central supply system, however, depending on the position of the servo control cylinder to be actuated, long supply lines are necessary which have a corresponding hydraulic volume and bring about a high weight. In addition, such a central hydraulic system has to include a plurality of valves to supply the various servo control cylinders with the respectively required hydraulic amount, which results in complex hydraulic systems.
In contrast to such a central supply system, decentralized actuator units have already been proposed which work with the assistance of so-called electrohydraulic actuators in which the respective servo control cylinder can be acted on by a decentralized pump which can be driven by an associated electric motor. In this connection, the electric motor and the pump as well as, optionally, also the servo control cylinder are combined into one assembly so that long hydraulic lines between the pump and the servo control cylinder can be saved. Such an electrohydraulic actuator is shown, for example, by U.S. Pat. No. 4,630,441 in which the electric motor, the pump and the servo control cylinder of the actuator are integrated into a common housing. In this context, the pump is configured as an axial piston pump which can be driven in opposite directions by the electric motor in order to be able to generate opposite actuation movements of the servo control cylinder depending on the direction of rotation of the motor. The pressure chambers of the servo control cylinder are connected to the pressure connections of the pump.
With such electrohydraulic actuator units, heating and temperature problems occasionally occur, in particular at the electric motor. WO 98/11358 suggests, for this purpose, using a liquid-cooled motor into which some of the hydraulic fluid provided by the pump is introduced to cool the motor. For this purpose, a valve arrangement is provided between the pump and the servo control cylinder and branches off some of the pressure fluid and introduces it into the electric motor to cool it. This additional valve arrangement, however, has to be controlled separately again and makes the construction of the actuator complicated; in addition, it brings along additional weight, which should be avoided in particular in the aerospace sector. In addition, the branching off of the pressure fluid for cooling purposes can impair the efficiency of the actuator unit.